Devices and Procedures
Medical devices are applied to the body to act on the body and the body will act on them but this does not mean such medical devices involve patenting any aspect of the body and this is the case with the device described herein. Millions of percutaneous transluminal angiographic (PTA) procedures are performed each year to treat occlusions, that are also called stenoses, in diseased coronary and peripheral arteries. The PTA procedure acts on an occluded/stenosed segment of an artery to open it so blood can flow through the previously occluded segment. The stenosis grows back at a rate that depends on many factors but across many conditions it returns to a sufficient extent to require another PTA in an average of 2½ years in 50% of cases. This restenosis may be delayed by placing any one of a variety of wire frameworks in the shape of an expandable tube called a stent to keep the artery propped open after the PTA. When a stent is added in a coronary artery the duration added to PTA alone is about 2½ years for a total duration of about 5 years until about 50% of occlusions/stenoses have grown back through the stent to re-instate the occlusion and require a repeat treatment so blood can flow. But in peripheral arteries where the legs are moving and the occlusions tend to be long, stents are likely to fracture, thus they add only marginally to the 2½ year duration of PTA treatment alone. Stent grafts were invented to provide a more flexible frame to avoid fracturing and a covering is added to resist re-stenosis through the frame. Such stent graft frames successfully avoid fracturing and their covers resist re-stenosis, but the stenosis tends to grow back around the stent graft ends in about the time that restenosis occurs through a bare stent thus a stent graft does not increase duration of treatment over that of a stent. This return of the stenosis around stent graft ends is called focal edge stenosis and occurs primarily at the proximal end. Though the exact causes are not well understood it is generally believed to involve blood flow dynamics and irritation to the artery wall which induces hyperplasia and rapid re-growth. The irritation may be rubbing, twisting or torsion, but only one means has been found to significantly reduce focal edge stenosis. That means is matching stent graft circumference and circumference of artery at landing sites in the previously occluded segment of artery. Unfortunately neither of the two common means of changing stent circumference is capable of achieving a stent circumference to match artery circumference. The most common means is a balloon inflated in the stent to increase its circumference. The result of this action is observed by the physician in a fluoroscopic X-ray image to determine when the stent and artery are the same size. In theory inflation is stopped when equal in size. But in practice the physician is looking at the artery segment that contains the stent and comparing it to the artery segment that does not contain the stent and it is not until the segment with the balloon and stent in it has overinflated enough for the physician to detect the difference that the physician stops increasing its size. Once this occurs, the balloon has increased the stent size to a greater circumference than that required for a match. After that, decreasing the balloon size does not decrease the stent circumference so the stent remains at the largest circumference the balloon reached even though the balloon decreases in size. Thus the desired match cannot be achieved once the balloon is over inflated. On average physicians overinflate by an average of about 20% before they recognize the difference in size. There was an experiment in which the amount of error was “over 20%” vs. “under 20%” difference in size and this was accomplished by sorting the cases after the fact to those under 20% and those over 20% larger than artery circumference. This was useful for determining that “under 20%” results in a significantly longer treatment duration than “over 20%” but provides no way of accomplishing the “under 20%” size before the fact. Another means a physician is provided to match circumference of stent graft and circumference of artery is by estimating the size of the artery before the stent graft is introduced into it. The type of stent used for this means of matching is one made of a nickel titanium compound and heat treated so it has a memory of a larger size that it will return to when heated to the temperature of the body. The delivery size is much smaller in circumference than the memory size. However the physician must estimate the memory size that will be needed. This is done by looking at the artery by fluoroscopic X-ray before the stent graft is introduced into the artery. Or ultra sound imaging may be substituted for fluoroscopic X-ray in an attempt to improve the estimate but this requires additional time and expertise and there are no data that indicate the extent to which this increases accuracy. The X-ray is an imprecise means of estimating and has not proven effective in bringing the error average to less than 20%. Another means of solving the error problem appears to be by providing a means of successive approximations by adjusting the stent graft size both up and down while the stent graft is in the artery under fluoroscopic X-ray examination. No stent graft currently provides the means of increasing and decreasing stent size in the artery. The present device is designed to increase and decrease in circumference a double spiral stent or stent graft by use of two somewhat different configurations. The stent or stent graft is designed to be increased and decreased in size while the stent/stent graft is in the artery where sizes can be directly compared by X-Ray fluoroscopy the physician uses to accurately compare the sizes of artery and stent/stent graft and adjust accordingly. This is unlike conventional stent grafts that do not provide any means to reduce the size once the physician has made it greater than artery size during the comparison. The present device provides, as does a prior art device by one of the inventors, to increase and decrease stent/stent graft size while it is in the artery. That device was revealed in U.S. Pat. No. 6,195,986 dated Aug. 19, 2013 titled “Suturing an Expanding, Contracting Graft Tube in Artery Segment Previously Occluded”. That revealed a single spiral stent/stent graft in which the single spiral is rotated to increase and decrease its circumference and included in the device is a means of suturing the stent graft ends to the artery at landing sites. The present device discloses a double spiral stent/stent graft which include means of changing their length and thus increasing and decreasing their circumference while in the artery until the operator is satisfied with the match between circumference of artery and double spiral stent/stent graft which is then it is locked to the desired length and circumference.
Advantages
1. Stent or stent graft is preselected to be the approximate circumference and length for treating the previously occluded artery then introduced into the artery to be fine tuned by increasing and decreasing the circumference to that of the artery in which it is located, as observed with X-Ray fluoroscopy while in the artery.
2. The length of the double spiral frame of the stent/stent graft is controlled in order to increase and decrease the circumference of the stent/stent graft while in the artery and thus to match the artery circumference.
3. The shape of the double spiral stent/stent graft may be tapered to match the taper of the artery in which it is placed to improve the fit of double spiral stent/stent graft and artery throughout their length in common.
4. There are concentric inner and outer spirals of wire that have their ends joined to form the double spiral stent/stent graft and equal and opposite torsion is created in each and by changing their length and circumference that torsion is counteracted thus conferring no torsion to artery.
5. The same spiral frame of attached concentric spiral wires may be used as a bare double spiral stent or covered with a PTFE cover to create a double spiral stent graft.
6. Flexibility of a spiral is greater than that of other stent designs thus a spiral stent best resists fracturing.
7 Two means of varying length are provided in alternative configurations, one requiring balloons on concentric catheters, with heat treated indents and detents on a control wire in a control tube and a second with a turning arm for screwing male threads on the control wire into female threads in the control tube and in each alternative configuration locking length which also locks circumference.
Key 1.Outer spiral 2.Inner spiral 3.Double spiral stent graft 4.Clips 5.Control tube 6.Control wire 7.Guidewire 8.Cover 9.Double spiral stent10.Distal balloon11.Proximal balloon12.Distal catheter13.Proximal catheter14.Clamp tube15.Indents detents16.Turning arm17.Fluid line18.Fluid port19.Threads20.Clamp holder21.Clamp22.Cooling balloon23.Hangers24.Holding flanges